Lancet Report Estimates 710,000 Heat-Related Deaths in 2023, Warns of Global Health Emergency

A major international health assessment has warned that climate change is causing increasingly severe harm to human health, estimating that extreme heat was associated with a record 710,000 deaths worldwide in 2023 and that rising temperatures are imposing particularly heavy economic costs on Africa and Southeast Asia.

The findings were published on Wednesday, October 28, in the tenth annual Lancet Countdown report on health and climate change, ahead of the COP31 United Nations climate summit in November.

The assessment was led by University College London and developed in strategic collaboration with the World Health Organization.

It brings together the work of 146 researchers from institutions around the world and examines 54 indicators covering health risks, economic impacts, climate adaptation and the benefits of action to reduce emissions.

According to the report, more than 70 percent of the estimated 710,000 heat-related deaths in 2023 were attributable to human-caused climate change.

The researchers arrived at those figures through statistical modelling and attribution analysis. They are estimates of the health burden associated with heat exposure, not a count of individual death certificates listing climate change as the cause.

Across the period from 2016 to 2023, the researchers estimated an annual average of approximately 540,800 heat-related deaths.

They attributed about 68 percent of those deaths to human-caused climate change, equivalent to nearly three million deaths over the eight-year period.

The findings represent an escalation in the health consequences of rising temperatures since the Paris Agreement was adopted in 2015.

The report estimates that annual average heat-related mortality increased by nearly 36 percent in the years following the agreement compared with the preceding decade.

Researchers warned that rising temperatures increase the risks of heat exhaustion, heatstroke, dehydration and complications involving the heart and kidneys.

Older people, outdoor workers, individuals with existing health conditions and communities with limited access to cooling and healthcare are particularly vulnerable.

The economic consequences are also substantial.

The Lancet Countdown estimates that heat exposure reduced potential working time by 573 billion hours globally in 2025, representing approximately $1.07 trillion in lost potential earnings.

That amount is an economic model's estimate of foregone income from reduced labour capacity, rather than money directly withdrawn from national budgets or an audited measure of total economic losses.

Agriculture and construction were among the sectors most affected because workers in those industries frequently undertake physically demanding activities outdoors.

Africa and Southeast Asia experienced particularly severe impacts.

According to the Potsdam Institute for Climate Impact Research, which contributed to the assessment, heat-related potential income losses in 2025 were equivalent to approximately 3.2 percent of Africa's gross domestic product and 3.9 percent of Southeast Asia's.

Europe's comparable estimated loss was 0.2 percent.

Agriculture accounted for 71 percent of Africa's estimated heat-related potential income losses.

The findings highlight a significant inequality: countries and communities that have contributed relatively little to historical greenhouse-gas emissions often face some of the greatest risks to their health, productivity and livelihoods.

For Nigeria and other African economies, the report reinforces concerns about the vulnerability of agricultural workers, informal businesses and communities with limited access to reliable electricity, clean water and healthcare.

Heat exposure can reduce the number of hours people can work safely, while drought and changing rainfall patterns can affect food production and household incomes.

The assessment does not establish that every African country experienced identical losses, and the regional figure should not be presented as Nigeria's individual GDP loss.

Beyond extreme heat, researchers found that 51.8 percent of the world's land experienced at least one month of extreme drought in 2025.

The report also identifies increasing risks associated with flooding, infectious diseases and pressure on food and water systems.

Its authors argue that the scale of these interconnected threats warrants recognition of climate change as a global health emergency.

That is a recommendation by the researchers, not an announcement that the World Health Organization has formally declared a public health emergency of international concern.

The WHO said the evidence demonstrated the need to place health at the centre of climate policy and strengthen systems capable of protecting vulnerable populations.

The report also identifies measurable progress.

Global investment in clean energy reached approximately $2.1 trillion in 2025, while improvements in air quality have helped prevent premature deaths in countries that have reduced pollution from fossil fuels.

More countries are also developing health adaptation plans and early-warning systems to prepare for climate-related emergencies.

However, researchers concluded that these improvements are not keeping pace with the accelerating risks.

The findings arrive shortly before COP31, when governments are expected to discuss climate action, adaptation financing and the implementation of international commitments.

For developing economies, the report strengthens the case for investment in heat-resilient healthcare facilities, safer working conditions, reliable electricity, water infrastructure and climate-sensitive disease surveillance.

It also raises questions about how international climate finance can better reach countries facing substantial health and economic risks.

The central conclusion is that climate change is already producing measurable health and economic consequences, rather than representing only a future environmental threat.

The figures published in the Lancet Countdown are research estimates based on available evidence and modelling, but their scale underscores the urgency of strengthening public health protections and reducing exposure to extreme heat.

The report's authors are calling for a coordinated international response that treats protecting human health as a central objective of climate policy.